(1) Summary of the Invention
The present invention relates to an improved collimator apparatus and method for focusing a beam from a radiation source. In particular the present invention relates to an apparatus which uses coil springs for locking nested rods together to define an opening for collimating the beam. Related U.S. application Ser. No. 850,486 describes a collimator apparatus which uses a clamping means to secure nested rods in position. This system works well; however, an improved means for moving and locking the rods to define the opening was needed.
(2) Prior Art
Collimator apparatus for focusing radiation are well known to the prior art. Most of these apparatus provide beams with a fixed cross-section which can be changed only by changing an insert which focuses the beam. This type of apparatus is cumbersome where the cross-section of the beam has to be repeatedly changed such as in patient treatment with radiation directed at a defined area of the body which is changed from patient to patient.
Variable collimator apparatus for radiation are also well known to the prior art. These apparatus provide a moveable interfering member in the beam. U.S. Pat. No. 4,463,266 to Brahme describes a collimator apparatus which uses wedge shaped slabs which move into the beam so as to define the beam. This apparatus is complicated and expensive to build because of the precision of the fit of the wedges relative to each other. Other prior art apparatus include camera or iris type lenses with uniformly change the diameter of the beam and thus are not suitable where the beam is to have an irregular cross-section. One prior art example is described in U.S. Pat. No. 4,534,052 to Milcamps. None of this prior art provides a means for rapidly and simply adjusting the beam cross-section non-uniformly.